tilelink2: add TLZero; /dev/zero suitable for putting behind locked cache ways

src/main/scala/uncore/tilelink2/Zero.scala

@@ -0,0 +1,44 @@
+// See LICENSE.SiFive for license details.
+
+package uncore.tilelink2
+
+import Chisel._
+import config._
+import diplomacy._
+
+class TLZero(address: AddressSet, executable: Boolean = true, beatBytes: Int = 4)(implicit p: Parameters) extends LazyModule
+{
+  val node = TLManagerNode(Seq(TLManagerPortParameters(
+    Seq(TLManagerParameters(
+      address            = List(address),
+      regionType         = RegionType.UNCACHED,
+      executable         = executable,
+      supportsGet        = TransferSizes(1, beatBytes),
+      supportsPutPartial = TransferSizes(1, beatBytes),
+      supportsPutFull    = TransferSizes(1, beatBytes),
+      fifoId             = Some(0))), // requests are handled in order
+    beatBytes  = beatBytes,
+    minLatency = 1))) // no bypass needed for this device
+
+  lazy val module = new LazyModuleImp(this) {
+    val io = new Bundle {
+      val in = node.bundleIn
+    }
+
+    val in = io.in(0)
+    val edge = node.edgesIn(0)
+
+    val a = Queue(in.a, 2)
+    val hasData = edge.hasData(a.bits)
+
+    a.ready := in.d.ready
+    in.d.valid := a.valid
+    in.d.bits := edge.AccessAck(a.bits, UInt(0))
+    in.d.bits.opcode := Mux(hasData, TLMessages.AccessAck, TLMessages.AccessAckData)
+
+    // Tie off unused channels
+    in.b.valid := Bool(false)
+    in.c.ready := Bool(true)
+    in.e.ready := Bool(true)
+  }
+}